The subject of this invention is an improvement for valve couplers designed to allow their connection despite the presence of considerable residual pressure in user lines.
The invention thus concerns the type of valve coupler comprising an outside tubular body, one end of which is provided with a solid coupling means to a soruce of fluid under pressure and which accommodates a tubular element free to move axially in both directions, whereby the rear end of the outside tubular element which matches the free end of the tubular valve body and comprises the female fitting of the coupler, accommodates the locking balls which are housed in an annular row of holes, whereby the balls are intended to be engaged in and located by an external annular groove provided for this purpose adjacent to the end of the male coupler fitting, whereby a spring acts to return this tubular element to a stable intermediate position in which the annular row of holes in which the locking balls are housed coincides in an axial plane with a radial internal rib with tapered faces provided in the tubular valve body in order to maintain the balls in their locking position, that is to say in a position in which they project radially inside the bore in the mobile tubular element, whereby the latter is provided with a valve towards its rear end, which is normally maintained in a closed position by means of a spring and is designed to be withdrawn to an open position by the valve of the male fitting whenever the latter is inserted in the female fitting.
In this type of coupler, each valve is associated with a return spring and a stop limiting the valve stroke which essentially corresponds to the half of the travel of the male fitting during insertion in the female fitting, which acts to maintain the two valves open by allowing them to bear on one another as long as the two fittings are connected.
With couplers of this type, if a considerable level of residual pressure is still present in the user lines, of the order of 200 bars, for example, the two valves simply cannot be allowed to open simultaneously before the male fitting is locked in position. However, the male fitting can usually only be locked after the two valves are fully open.
One solution is to provide the valve located on the supply side with a stroke double that of the valve on the user side, whereby the latter would open as soon as the supply pressure exceeds the residual pressure in the user line. However, if a flow reversal were to occur during operation and a high viscosity hydraulic coil were to be used, there would be a risk of forcing the valve located on the user side to close and to remain firmly closed as a result of the pressure balance prevailing on its two sides.
Attempts have been made to deal with this disadvantage by doubling the opening stroke of the valve located on the supply side, on the one hand and by preventing the valve on the user side from returning to its closed position at all, until the coupler is disconnected.
French document No. 2,384,196 provides a description of a coupling of this type where the stroke stop associated with the valve on the supply side is arranged so that it goes into a holding mode prior to being locked in position after a single opening stroke, whereby it is locked in a position in which it is limited to a single opening stroke and to a single operation by the return of the valve to a position corresponding to a single stroke and is maintained in a retracted position allowing the valve to travel twice its normal stroke as soon as the two coupling elements are uncoupled.
In this coupling, the stroke stop associated with the valve on the supply side comprises a pin housed in the valve body of the corresponding element of the coupling, which is actuated by a radial spring in the direction of the stem of the valve, wherby the rear end of the valve stem is narrower and the inside shoulder of the narrower part of this valve stem is designed to contact the aforesaid actuating pin in order to limit the opening stroke of the valve to a single stroke length. In order to allow the valve to perform a double opening stroke whenever the two coupling elements are connected to one another, the narrower rear end of the valve stem is provided with a cylindrical collar whose outside diameter slightly exceeds the larger diameter of the valve stem, the end of which facing the valve itself is truncated.
In this way, as soon as the male fitting engages in the female fitting of this coupler, only the valve on the supply side is brought to an open position and it is retracted beyond its normal opening stroke by the valve on the user side, since its normal stroke stop is in its retracted position.
Following this, when the supply line is opened, the supply pressure which exceeds the residual pressure remaining in the supply line, will act to open the valve on the user side, normal flow will occur and the stroke stop associated with the valve on the supply side will be returned to its active position, whereby the return spring in this valve will return the latter to its normal opening position, that is to say, resting against its stroke stop.
However, satisfactory operation of this valve requires that the friction forces between the collar and the radial actuating pin, exceed the forces arising between the collar and the narrower diameter of the valve stem, since, if this were not the case, the valve would be entirely unable to perform a double stroke. It is easy to imagine that the wear resulting from repeated coupling and uncoupling operations would be sufficient to reverse the relation between the aforesaid frictional forces and thus render the retractable actuating pin inoperative.